From d4236f1ef270347b26ed34bcd0eb28d285b86bcb Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Fri, 23 Jan 2026 19:16:33 +0000 Subject: [PATCH] arm64: Add MT_S2{,_FWB}_AS_S1 encodings pKVM usage of S2 translation on the host is purely for isolation purposes, not translation. To that effect, the memory attributes being used must be that of S1. With FWB=0, this is easily achieved by using the Normal Cacheable type (which is the weakest possible memory type) at S2, and let S1 pick something stronger as required. With FWB=1, the attributes are combined in a different way, and we cannot arbitrarily use Normal Cacheable. We can, however, use a memattr encoding that indicates that the final attributes are that of Stage-1. Add these encoding and a few pointers to the relevant parts of the specification. It might come handy some day. Reviewed-by: Joey Gouly Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Link: https://patch.msgid.link/20260123191637.715429-2-maz@kernel.org Signed-off-by: Marc Zyngier --- arch/arm64/include/asm/memory.h | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h index 9d54b2ea49d66..a2b7a33966ff1 100644 --- a/arch/arm64/include/asm/memory.h +++ b/arch/arm64/include/asm/memory.h @@ -175,19 +175,24 @@ #define MT_DEVICE_nGnRE 4 /* - * Memory types for Stage-2 translation + * Memory types for Stage-2 translation when HCR_EL2.FWB=0. See R_HMNDG, + * R_TNHFM, R_GQFSF and I_MCQKW for the details on how these attributes get + * combined with Stage-1. */ #define MT_S2_NORMAL 0xf #define MT_S2_NORMAL_NC 0x5 #define MT_S2_DEVICE_nGnRE 0x1 +#define MT_S2_AS_S1 MT_S2_NORMAL /* - * Memory types for Stage-2 translation when ID_AA64MMFR2_EL1.FWB is 0001 - * Stage-2 enforces Normal-WB and Device-nGnRE + * Memory types for Stage-2 translation when HCR_EL2.FWB=1. Stage-2 enforces + * Normal-WB and Device-nGnRE, unless we actively say that S1 wins. See + * R_VRJSW and R_RHWZM for details. */ #define MT_S2_FWB_NORMAL 6 #define MT_S2_FWB_NORMAL_NC 5 #define MT_S2_FWB_DEVICE_nGnRE 1 +#define MT_S2_FWB_AS_S1 7 #ifdef CONFIG_ARM64_4K_PAGES #define IOREMAP_MAX_ORDER (PUD_SHIFT) -- 2.47.3